This invention relates to an improvement for an endless belt for transmitting power from a driving pulley to a driven pulley. More particularly it relates to a power transmission belt for heavy loads, which transmit great torque from a driving pulley mounted on a driving shaft to a driven pulley mounted on a driven shaft.
An object of this invention is to improve the flexibility, side pressure durability and crack resistance of a power transmission belt. Also, it is an object of this invention to eliminate drawbacks such as vibration, removal and turning-over accompanying a conventional multi-V-belt drive system, and to eliminate power transmission loss due to the unequal lengths of plural belts. Hence, this invention seeks to increase the service life of a power transmission belt.
In the aforementioned multi-V-belt drive system, generally a plurality of power transmission V-belts are laid over a single pulley having a plurality of pulley grooves, and the V-belts are liable to be of different length. Therefore, loads applied to the V-belts are different, and accordingly loads are collectively applied to a particular belt among the belts. As a result the life of that belt is shortened. Furthermore, in the case where a machine such as a crusher or a compressor having a great impact force is driven by the multi-V-belt system, the belts are vibrated and are brought into contact with adjacent belts. As a result the belt or belts may be turned over or may be dropped off the pulley.
In order to overcome these difficulties, a power transmission belt has been proposed by U.S. Pat. No. 3,404,577 issued to Zahn, in which the upper surfaces of plural V-belt bodies are connected by an elastomer tie band in which a plurality of nylon cords substantially 90.degree. with the longitudinal axis of the belt are embedded. This conventional belt is excellent in flexibility in the longitudinal direction of the belt. However, where the belt is used with a small diameter pulley, the rubber between the cords, which forms the tie band, repeatedly excessively elongated in the longitudinal direction. Hence, it is liable to be cracked. Since the nylon cords are extended in the widthwise direction of the belt, the belt is rigid in the widthwise direction, but it is low in stretchability. Thus, the belt cannot sufficiently follows motions in the widthwise direction thereof.
In addition, U.S. Pat. No. 3,564,933 issued to Clinkenbeard disclose a belt in which the upper surfaces of V-belt bodies are connected by a tie band which is obtained by embedding wide angle cloth in an elastomer material. Since the tie band includes the wide angle cloth, the tie band is relatively high in stretchability in the lengthwise and widthwise directions of the belt. However, when the belt is used with a small diameter pulley, it still suffers from the following disadvantages. The wide angle cloth is a fabric made up of warps and wefts, and the warps and wefts intersect with one another. Therefore, as the belt is bent on a small diameter pulley, the tie band is elongated considerably in the longitudinal direction of the belt and simultaneously the wide angle cloth of the tie band is also elongated. In this operation, the warps and the wefts are abraded by each other, and they are easily damaged.
The warps and wefts of the wide angle cloth are extended in a wavy state during weaving. Therefore, the rigidity, in the widthwise direction of the belt, of the wide angle cloth is not as high as expected. Accordingly, the V-belt bodies are dropped in the pulley grooves, as a result the service life of the belt is relatively short.